In-process monitoring, automated decision-making, and process control for composite manufacturing using part-referenced ply-by-ply infrared thermography and other non-contact non-destructive inspection

ABSTRACT

Method and apparatus for detecting defects in a composite is provided. After a ply of material for a workpiece is positioned, thermal energy is applied to a top surface of the ply of material, and a digital thermographic camera captures images of the top surface. A computer processor determines heat characteristics of the top surface to identify regions of the top surface with different heat characteristics. Such different areas are identified as regions that include a defect. The defect regions can be repaired prior to disposing additional plies of material over previously-applied plies.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 15/623,367, filed Jun. 16, 2017, issued as U.S. Pat. No.10,061,771, which is a continuation of U.S. patent application Ser. No.14/961,494, filed Dec. 7, 2015, issued as U.S. Pat. No. 9,709,443. Theaforementioned applications are herein incorporated by reference.

BACKGROUND

Aspects described herein relate to flaw detection in compositelaminates, and more specifically, to detecting flaws in green compositematerials, which are composite materials that have not yet been cured.

SUMMARY

According to one aspect, a method includes laying a first ply ofmaterial, applying thermal energy to a surface of the first ply ofmaterial, and capturing at least one digital thermographic image of thesurface of the first ply of material after applying the thermal energy.Using a computer processor, at least one heat characteristic of regionsof the first ply of material in the at least one digital thermographicimage is analyzed to identify defect regions in which the at least oneheat characteristic is different than baseline data. Upon identifying adefect region, an alert is output and processing is halted to allow thedefect region to be corrected. Processing is resumed and a second ply ofmaterial is laid on the first ply of material after resuming processing.

According to one aspect, a system includes a work surface for arrangingand compacting uncured composite layers, a heat source arranged relativeto the surface and operable to provide thermal energy to a surface of afirst ply of material on the work surface, and a thermographic digitalcamera arranged relative to the surface and operable to capture at leastone digital thermographic image of the surface of the first ply ofmaterial. The system also includes a computer processor in communicationwith the thermographic digital camera and the heat source, and acomputer memory containing a program that, when executed on the computerprocessor, performs an operation for processing data. The operation forprocessing data comprises applying thermal energy to a surface of thefirst ply of material, capturing at least one digital thermographicimage of the surface of the first ply of material after applying thethermal energy, and analyzing at least one heat characteristic ofregions of the first ply of material in the at least one digitalthermographic image to identify defect regions in which the at least oneheat characteristic is different than baseline data. Upon identifying adefect region, an alert is output and processing is halted to allow thedefect region to be corrected. Processing is resumed and a second ply ofmaterial is laid on the first ply of material after resuming processing.

According to one aspect, a method includes laying a first ply ofmaterial, applying thermal energy to a surface of the first ply ofmaterial, and capturing at least one digital thermographic image of thesurface of the first ply of material after applying the thermal energy.Using a computer processor, at least one heat characteristic of regionsof the first ply of material is analyzed in the at least one digitalthermographic image to identify defect regions in which the at least oneheat characteristic is different than baseline data. Upon identifying adefect region, an alert is output, the defect region is corrected; and asecond ply of material is laid on the first ply of material afterresuming processing.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1A is a perspective view of a layup table with four plies ofcomposite sheets of a laminate laid out on a surface of the table,wherein three of the four plies are shown partially cut away to displaythe underlying plies;

FIG. 1B is a cross-sectional side view of the four plies of the laminateof FIG. 1A with a disbond between the second and third plies;

FIG. 1C is a cross-sectional side view of the four plies of the laminateof FIG. 1A with an inclusion between the second and third plies;

FIG. 2 is a block diagram of a system for detecting defects in alaminate of uncured, compacted composite sheets, wherein the system isshown detecting defects in the laminate shown in FIG. 1A as an exemplaryscenario;

FIG. 3 is a flow chart of a process for detecting a defect in a laminateof uncured, compacted composite sheets;

FIG. 4 is a flow chart of a process for building a laminate of compactedcomposite sheets;

FIG. 5A is a chart illustrating a temperature response over time for adefect-free laminate of uncured, compacted composite sheets and alaminate of uncured, compacted composite sheets having a conductiveinclusion;

FIG. 5B is a chart illustrating a temperature response over time for adefect-free laminate of uncured, compacted composite sheets and alaminate of uncured, compacted composite sheets having a disbond and/oran inclusion;

FIG. 6A is a chart illustrating a first derivative of the temperatureresponse over time for the defect-free laminate of uncured, compactedcomposite sheets and the laminate of uncured, compacted composite sheetshaving the conductive inclusion shown in FIG. 5A;

FIG. 6B is a chart illustrating a first derivative temperature responseover time for the defect-free laminate of uncured, compacted compositesheets and the laminate of uncured, compacted composite sheets havingthe disbond and/or insulative inclusion shown in FIG. 5B;

FIG. 7A is a chart illustrating a second derivative of the temperatureresponse over time for the defect-free laminate of uncured, compactedcomposite sheets and the laminate of uncured, compacted composite sheetshaving the conductive inclusion shown in FIG. 5A;

FIG. 7B is a chart illustrating a second derivative temperature responseover time for the defect-free laminate of uncured, compacted compositesheets and the laminate of uncured, compacted composite sheets havingthe disbond and/or insulative inclusion shown in FIG. 5B; and

FIG. 8 is a flow chart of a process for detecting a defect, according toanother aspect of the disclosure.

DETAILED DESCRIPTION

In the following, reference is made to aspects presented in thisdisclosure. However, the scope of the present disclosure is not limitedto specific described aspects. Instead, any combination of the followingfeatures and elements, whether related to different aspects or not, iscontemplated to implement and practice contemplated aspects.Furthermore, although aspects disclosed herein may achieve advantagesover other possible solutions or over the prior art, whether or not aparticular advantage is achieved by a given aspect is not limiting ofthe scope of the present disclosure. Thus, the following aspects,features, and advantages are merely illustrative and are not consideredelements or limitations of the appended claims except where explicitlyrecited in a claim(s). Likewise, reference to “the invention” or “thedisclosure” shall not be construed as a generalization of any inventivesubject matter disclosed herein and shall not be considered to be anelement or limitation of the appended claims except where explicitlyrecited in a claim(s).

Structures, such as wing spars and fuselage barrel sections of aircraftcan be made with composite materials. The composite materials aretypically formed as a laminate of several plies of composite sheets.After the plies of composite sheets are laid out, the resulting laminateis cured. After curing, the laminate is checked for defects, such asdisbonds (i.e., regions in which two adjacent plies do not bond togetherresulting in a void) and inclusions (i.e., regions in which foreignobject debris is between two adjacent plies). To correct such defects,the region with the defect is scarfed out to remove the defect and apatch of plies is installed in the scarfed out area. The patch is thencured and the rechecked for any additional defects. Such a repairprocedure can be expensive and time consuming.

FIG. 1A is a perspective view of a layup table 102 with a laminate 110that includes four plies of composite sheets 112, 114, 116, and 118arranged on a work surface 104 of the layup table 102. The top threeplies of composite sheets 114, 116, and 118 are shown in partial cutawayto illustrate the underlying plies. The four plies are arranged inalternating directions. The first ply 112 includes fibers (e.g., carbonfibers) arranged in a first direction, the second ply 114 includesfibers arranged in a second direction that is orthogonal to the firstdirection, the third ply 116 includes fibers arranged in the firstdirection, and the fourth play includes fibers arranged in the seconddirection. In practice, a person or a machine would lay the first ply112 on the work surface 104 of the layup table 102 with the fibers ofthe first ply 112 arranged in the first direction. The person or machinewould then lay the second ply 114 on the first ply 112 with the fibersof the second ply 114 arranged in the second direction. The person ormachine would then lay the third play 116 on the second ply 114 with thefibers of the third ply 116 arranged in the first direction. The personor machine would then lay the fourth ply 118 on the third ply 116 withthe fibers of the fourth ply 118 arranged in the second direction. Afterthe plies 112, 114, 116, and 118 have been laid on the work surface 104,the plies 112, 114, 116, and 118 can be compacted using rollers or thelike. In various circumstances, additional plies could be laid on top ofthe illustrated four plies 112, 114, 116, and 118 and compacted. Also,in various circumstances, the number of plies that are laid down beforea compaction step can be more or fewer than the illustrated four plies.

After compaction, it is possible for defects to exist in the uncured,compacted composite sheets. FIG. 1B illustrates an example of a disbond120. As shown in FIG. 1B, the disbond 120 is formed where the second ply114 and the third ply 116 were not compacted together. If a disbond 120occurs, then the second ply 114 and the third ply 116 will not adhere toone another during a subsequent curing process. FIG. 1C illustrates anexample of an inclusion 122, in which a foreign object is arrangedbetween plies. As shown in FIG. 1C, the inclusion 122 is between thesecond ply 114 and the third ply 116. The inclusion could be a piece ofbacking paper for the second ply 114 or the third play 116 that was notremoved, for example. The inclusion 122 can form disbonds 124 alongedges of the inclusion 122 where the inclusion 122 prevents the adjacentplies (e.g., plies 114 and 116) from joining together. If the inclusion122 is not removed, then the second ply 114 and the third ply 116 willnot adhere to one another during the subsequent curing process. Invarious instances, the inclusion could be a conductive inclusion, whichmeans that the inclusion transfers heat at a faster rate than the plies112, 114, 116, and 118 of the laminate 110. For example, a conductiveinclusion could be a metallic particle, such as a metal foil. In variousother instances, the inclusion could be an insulative inclusion, whichmeans that the inclusion transfers heat at a slower rate than the plies112, 114, 116, and 118 of the laminate 110. For example, an insulativeinclusion could be a piece of backing paper. In various instances, theinclusion could be a neutral inclusion, which means that the inclusiontransfers heat at the same rate as the plies 112, 114, 116, and 118 ofthe laminate 110. For example, a neutral inclusion could be a piece ofanother ply.

Laminates, such as the laminate 110 shown in FIGS. 1A-1C, are currentlyinspected after the curing process using ultrasound. If a defect isfound, the region of the cured laminate is scarfed out to remove thedefect. Typically, the scarfed out region has a diameter of at leasttwenty times the size of the defect. Thus, a defect that is 0.1centimeters across would be repaired with a scarfed out region having adiameter of two centimeters, for example. After the defect has beenscarfed out of the cured laminate, a patch of uncured composite sheetsis fit into the scarfed out region, compacted, and then cured in place.The repaired area is then inspected again to check for additionaldefects. Such a repair process is time consuming, especially if multipledefects are found in a laminate.

FIG. 2 illustrates a system 200 for detecting defects in a laminate,such as disbonds and inclusions, before the laminate is cured. Forpurposes of illustration, the system 200 is described with reference tothe laminate 110 discussed above with reference to FIGS. 1A-1C. However,the system 200 could be used on other laminates. If a defect is detectedprior to the laminate 110 being cured, the defect can be repaired fasterand cheaper. For example, a region that includes a detected disbondcould be compacted again to remove the disbond. As another example, theplies could be separated in a region that includes a detected inclusionto remove the inclusion. The plies could then be put back in place andcompacted again. Such repairs could be performed more quickly and lessexpensively than repairs after the laminate 110 is cured.

The system 200 includes a heat source 214, such as a heat lamp or a heatgun. The heat source 214 applies a burst of heat (i.e., a momentary heatload) to a top surface 111 of the laminate 110 to increase thetemperature of the top surface 111 of the laminate 110 by a smallamount. For the laminate 110 described in greater detail above, the heatsource 214 would apply to the top-facing surface of the fourth ply 118.For example, the heat source 214 may apply heat to the top surface 111of the laminate 110 to increase the temperature of the top surface 111by a few degrees or less. In any case, the heat source 214 does notapply enough heat to cause the laminate 110 to begin to cure. Dependingon the size of the laminate 110, the heat source 214 could be an arrayof heat sources arranged over the laminate 110 to provide uniform heatapplication to the top surface 111 of the laminate 110. As described ingreater detail below, in various aspects, the heat source 214 could bemovable in the directions of arrows 216 and 218 to apply heat todifferent locations along the top surface 111 of the laminate 110.

The system also includes a digital thermographic camera 212 thatcaptures images of thermal properties (e.g., temperature) and changes tothe thermal properties of the top surface 111 of the laminate 110 afterthe heat source 214 applies the momentary heat load. For example, thedigital thermographic camera 212 could be an infrared camera. After heatis applied to the top surface 111 of the laminate 110 by the heat source214, the heat travels from the top surface 111 through the laminate 110.The rate of heat transfer from the top surface 111 to internal layers ofthe laminate 110 is affected by defects, such as the disbonds andinclusions discussed above with reference to FIGS. 1B and 1C, whichobstruct the flow of heat from the top surface 111 into the laminate110. By capturing successive images of heat characteristics of the topsurface 111 of the laminate 110 after the application of heat by theheat source 214, disbonds and inclusions (and other flaws) can bediscovered. For example, the heat characteristics of the top surface 111could be temperatures of the surface at different regions and/ordifferent times, a first derivative of the temperature (i.e., rate ofchange of the temperature of the top surface 111) and/or a secondderivative of the temperature (i.e., rate of change of the rate ofchange of the temperature of the top surface 111). In various aspects,the digital thermographic camera 212 could be movable in the directionsof arrows 216 and 218. In certain aspects, the digital thermographiccamera 212 and the heat source 214 move in the directions of arrows 216and 218 together.

The heat source 214 and thermographic camera 212 are in communicationwith a computer 220. The computer 220 includes a computer processor 222and computer memory 224. The digital thermographic camera 212 cantransmit captured images of thermal properties of the top surface 111 ofthe laminate 110 to the computer 220 for storage on the computer memory224. In operation, the computer processor 222 sends control signals tothe heat source 214 to trigger the momentary heat output to the topsurface 111 of the laminate 110. The computer processor 222 also sendscontrol signals to the digital thermographic camera 212 to trigger thedigital thermographic camera 212 to capture images of thermal propertiesof the top surface 111 laminate 110. The computer 220 can controlmovement of the heat source 214 and/or the digital thermographic camera212 in the directions of arrows 216 and 218.

The computer memory 224 can also store a heat transfer detection program226 that, when executed by the computer processor 222, triggers thedigital thermographic camera 212 and the heat source 214 and processesthe stored images of thermal properties of the top surface 111 of thelaminate 110. The heat transfer detection program 226 can determine heatcharacteristics at the different locations of the top surface 111 of thelaminate 110. The heat characteristics include at least one oftemperatures at different locations of the top surface 111 of thelaminate 110, a rate of change of temperatures (first derivative oftemperature) at the different locations of the top surface 111 of thelaminate 110, and a rate of change of the rate of change of temperatures(second derivative of temperature) at the different locations of the topsurface 111 of laminate 110. The temperature, first derivative oftemperature, and/or second derivative of temperature for the top surface111 of the laminate 110 can be determined over a period of time toidentify regions of the top surface 111 of the laminate 110 that havedifferent heat transfer properties from the remainder of the laminate110. As discussed, disbonds and/or inclusions (and other defects) in thelaminate 110 can change the rate of heat transfer relative to regions ofthe laminate 110 that do not include such defects. For a typicallaminate (e.g., laminate 110) that may have only a few defects, themajority of the top surface of the laminate will have the same or verysimilar heat characteristics. The regions of the laminate that includedefects will have different heat characteristics. By identifying regionsof the laminate 110 where the heat characteristics of the top surface111 differ from other regions, the locations of defects can beidentified.

The system 200 can include a display 228 in communication with thecomputer 220. In the event a defect is detected in the laminate 110 bythe computer 220, the display 228 could output an alert or alarm. Thedisplay 228 and could provide an indication of a location of thelaminate 110 that includes the defect. For example, the display 228could be a computer display screen that flashes to indicate a detecteddefect and that provides coordinates and/or a graphical depiction of alocation of the defect on the laminate 110.

FIG. 3 is a flowchart for a process 300 for detecting and correctingdefects in a laminate (e.g., the laminate 110) prior to curing thelaminate. In block 302, a burst of thermal energy is applied to asurface of a plurality of uncured compacted composite layers (e.g., thecomposite sheets 112, 114, 116, and 118 shown in FIGS. 1A-1C). Asdiscussed above, the burst of thermal energy can be applied by the heatsource 214 of the system 200, shown in FIG. 2. In block 304, at leastone digital thermographic image of the surface of the uncured compactedcomposite layers is captured. As discussed above, the least one digitalthermographic image captured by the digital thermographic camera 212 ofthe system 200, shown in FIG. 2. In block 306, the at least one digitalthermographic image can be analyzed to identify at least one heatcharacteristic of regions of the uncured compacted composite layers toidentify defect regions in which the at least one heat characteristic isdifferent than surrounding regions. As discussed above, the heattransfer detection program 226 executing on the computer processor 222of the system could analyze the at least one digital thermographic imagestored in computer memory 224 to identify at least one heatcharacteristic, which could be a temperature over time, a firstderivative of temperature over time, and/or a second derivative oftemperature over time of the top surface 111 of the laminate 110. Inblock 308, upon identifying a defect region, and alarm or alert isoutput. As discussed above, the display 228 of the system 200 coulddisplay such an alarm or alert. In block 310, a repair is performed onthe defect region of the uncured compacted composite layers. Forexample, if the defect in the defect region is known to be or believedto be a disbond, then additional compaction steps could be performed toeliminate the disbond. As another example, if the defect in the defectregion is known to be or believed to be an inclusion, then layers of thelaminate 110 can be at least partially removed to reveal the inclusion,the inclusion could be removed, and the layers could be replaced.Thereafter, an additional compaction procedure could be performed tore-compact the layers that had been removed. In block 312, afterdetected defects have been repaired, the laminate 110 can be cured.

FIG. 4 is a flowchart for a process 404 assembling a laminate thatincludes a plurality of layers. In block 402, a plurality of uncuredcomposite layers are arranged and compacted. In block 404, a burst ofthermal energy is applied to a surface of a plurality of uncuredcompacted composite layers (e.g., the composite sheets 112, 114, 116,and 118 shown in FIGS. 1A-1C). As discussed above, the burst of thermalenergy can be applied by the heat source 214, shown in FIG. 2. In block406, at least one digital thermographic image of the surface of theuncured compacted composite layers is captured. As discussed above, theleast one digital thermographic image captured by the digitalthermographic camera 212, shown in FIG. 2. In block 408, the at leastone digital thermographic image can be analyzed to identify at least oneheat characteristic of regions of the uncured compacted composite layersto identify defect regions in which the at least one heat characteristicis different than surrounding regions. As discussed above, the at leastone heat characteristic could be a temperature over time, a firstderivative of temperature over time, and/or a second derivative oftemperature over time of the top surface 111 of the laminate 110. In theevent no defects are found, then the process 400 could return to block402, if necessary, to arrange and compact additional uncured compositelayers on the laminate. Blocks 402, 404, 406, and 408 could be repeateduntil the laminate includes a suitable number of uncured compositelayers. The number of uncured composite layers added with each iterationof blocks 402, 404, 406, and 408 of the process 400 can vary dependingon various circumstances. In some circumstances, as few as one or twolayers may be added with each iteration through blocks 402, 404, 406,and 408. In other circumstances, as many as four, five, or more uncuredcomposite layers could be added with each iteration through blocks 402,404, 406, and 408. As discussed in greater detail below, certain heatsources and digital thermographic cameras may have sufficientsensitivity to detect defects that are three, four, or more layers deepin a laminate of uncured, compacted composite layers whereas other heatsources and digital thermographic cameras may be limited to detectingdefects that are one or two layers deep. Thus, the number of layersadded with each iteration through blocks 402, 404, 406, and 408 could bedependent on the type of heat source and/or digital thermographic cameraused in blocks 404 and 406.

In at least one aspect, blocks 402, 404, 406, and 408 could be performedin a continuous manner. For example, in at least one aspect, thelaminate could be applied around a cylindrical mandrel by wrapping acontinuous composite sheet around the mandrel. As the continuouscomposite sheet is laid on the mandrel (and on top of portions of thecontinuous sheet that have already been laid on the mandrel), thecomposite sheet is compacted (e.g., by a roller). The heat source anddigital thermographic camera could follow behind the compactingapparatus to analyze the compacted uncured laminate for defects.

In block 410, upon identifying a defect region, and alarm or alert isoutput. In block 412, a repair is performed on the defect region of theuncured compacted composite layers. For example, if the defect in thedefect region is known to be or is most likely a disbond, thenadditional compaction steps could be performed to eliminate the disbond.As another example, if the defect in the defect region is known to be oris most likely an inclusion, then layers of the laminate 110 can beremoved to reveal the inclusion, the inclusion could be removed, and thelayers could be replaced. Thereafter, additional compaction procedurecould be performed to re-compact the layers that had been removed. Afterthe defects have been removed, the process 400 can optionally return toblock 402 to arrange and compact additional uncured composite layers.

In block 416, after all of the uncured composite layers have beenarranged in compacted and any detected defects have been repaired, thelaminate 110 can be cured.

FIGS. 5A-5B illustrate temperature profiles that may be detected by adigital thermographic camera, such as the digital thermographic camera212 shown in FIG. 2. FIG. 5A illustrates the differences in temperatureof the top surface 111 of the laminate 110 over time for a defect-freeregion of the laminate and a region that has a conductive inclusion. Asexplained above, a conductive inclusion is an inclusion (e.g., debris)that conducts heat more readily than the laminate layers. For example, apiece of metal caught between layers of the laminate could be aconductive inclusion. After a heat source, such as the heat source 214shown in FIG. 2, outputs a burst of energy directed toward the topsurface 111 of the laminate 110, the temperature of the top surface 111of the laminate 110 rises. The chart 500 in FIG. 5A includes a solidline 502 indicating the normal (i.e., defect free) region of thelaminate and a broken line 510 indicating the region that has aconductive inclusion. The left-hand ends of the solid line 502 and thebroken line 510 indicate the temperature of the top surface 111 of thelaminate 110 immediately after the burst of energy from the heat source214 is applied to the top surface 111. Energy absorbed by the topsurface 111 has caused the temperature of the top surface 111 toincrease. After the initial increase in temperature of the top surface111, the temperature of the top surface 111 begins to decrease in alinear manner as the heat energy applied to the top surface 111 travelsdeeper into the laminate via conduction (as indicated by first portion504 of the solid line 502). The initial rate of heat transfer away fromthe top surface 111 via conduction is substantially the same for boththe normal region and the region that includes the inclusion, asindicated by the initial overlap of the solid line 502 and the brokenline 510.

Referring to the normal region, indicated by the solid line 502, as theheat energy reaches a bottom side of the laminate 110, the heat energycan travel no further through the laminate via conductance. Thereafter,the heat transfer away from the top surface 111 slows, as indicated bythe kink 506 and the reduced-slope second portion 508 of the solid line502.

Referring to the conductive inclusion region, indicated by the brokenline 510, before the heat energy reaches the bottom side of the laminate110, the heat energy encounters the conductive inclusion (e.g., theinclusion 122 shown in FIG. 1C could be a conductive inclusion). Theexemplary conductive inclusion provides additional mass that can act asa heat sink for the laminate such that heat from the top surface 111 canbe transferred to the inclusion via conductance. Furthermore, becausethe exemplary conductive inclusion is more conductive than thesurrounding layers of laminate, the top surface 111 of the laminate 110over the conductive inclusion cools faster than surrounding regions ofthe top surface 111. This faster cooling of the top surface 111 isindicated by a first kink 512 of the broken line 510 as the broken line510 deviates from the solid line 502. As the conductive inclusion warms,the heat transfer from the top surface 111 slows, and the broken line510 has a second kink 514. After the second kink 514, the rate oftemperature change of the top surface 111 over the conductive inclusionis substantially equal to the rate of temperature change of the topsurface 111 over normal regions of the laminate 110, as indicated byportion 504 of the solid line 502, as indicated by the portion 516 ofthe broken line 510. Because the conductive inclusion transfers heataway from the top surface 111 faster, the heat reaches the back surfaceof the laminate 110 at the conductive inclusion faster than atsurrounding normal regions. Thereafter, the heat transfer away from thetop surface 111 over the conductive inclusion slows, as indicated by thekink 518 in the broken line, which eventually joins the second portionof the solid line 502 (at the point indicated by reference numeral 520).

For a laminate that is only three, four, or five layers thick, the kinks506 and 518 in the temperature profiles for a normal region and a regionthat includes a conductive inclusion may be observable in a reasonableperiod of time. For example, the kinks 506 and 518 may occur withinthree to ten seconds after heat is applied to the top surface 111 of thelaminate 110. However, in instances in which the laminate is thicker(e.g., including tens of layers, such as fifty layers, one hundredlayers, or one hundred and fifty layers), the kinks 506 and 518 may notbe observable in a suitable period of time for such an inspection. Insuch instances, the kink 512 and/or the kink 514 in the temperatureprofile of the top surface 111 over the conductive inclusion should beperceivable. The kink 506 in the temperature profile of the top surface111 over normal regions does not need to be observed. For example,assuming that most of the laminate 110 is free from defects, thetemperature profile over time would be substantially homogenous.However, if a particular region includes a conductive inclusion, thatregion would have a temperature profile that decreases at a faster rate(at the kink 512) than the defect free regions. Thus, observing atemperature profile decreasing at a faster rate than surrounding regionscould indicate the presence of a conductive inclusion in the laminate110.

FIG. 6A illustrates a chart 600 showing a calculated first derivative ofthe temperature (i.e., a rate of change of temperature) of the topsurface 111 of laminate 110 for the defect free (i.e., normal) region,indicated by the solid line 602, and of the region that has theconductive inclusion, discussed above with reference to FIG. 5A,indicated by the broken line 610. As shown in FIG. 6A, the firstderivative of temperature for the normal region is a first rate ofchange, indicated by portion 604 of the solid line 602, whichcorresponds with the first portion 504 of the solid line 502 in FIG. 5A.Since the temperature of the top surface 111 is decreasing, the valuesof the first derivative are negative. Stated differently, a zero valueon the temperature axis of the chart 600 is above the illustrated solidline 602 and the broken line 610. When the temperature profile of thetop surface 111 over the normal region reaches the kink 506 in FIG. 5A,the first derivative of temperature for the normal region increases(toward zero), as indicated by the portion 606 of the solid line 602.Thereafter, the first derivative of temperature for the normal regionsettles at a second rate of heat transfer, as indicated by the portion608 of the solid line 602. The first derivative of temperature for theregion that includes the conductive inclusion diverges from the firstderivative of temperature for the normal region twice. First, where thetemperature profile of the top surface 111 for the conductive inclusiondecreases faster than surround normal regions at the kinks 512 and 514(in FIG. 5A), the first derivative of temperature decreases (away fromzero) from the first rate of change (indicated by the portion 604 of thesolid line 602) at the point indicated by reference numeral 612, reachesa peak at the point indicated by reference numeral 614, and thenincreases (toward zero) at the point indicated by reference numeral 616.When the temperature profile of the top surface 111 over the conductiveinclusion reaches the kink 518 in FIG. 5A, the first derivative oftemperature increases (toward zero) at the point indicated by referencenumeral 618 and as indicated by the portion 620 of the broken line 610.Thereafter, the first derivative of temperature for the conductiveinclusion settles at the second rate of heat transfer, as indicated bythe portion 622 of the broken line 610.

As discussed above, in instances in which only a few layers of laminatehave been laid out, the kinks 506 and 518 of the temperature profilesfor the normal regions and conductive inclusions may be perceivable in asuitable period of time for an inspection. In other instances in whichmany layers of laminate have been laid out, the kinks 506 and 518 maynot be perceivable in a suitable period of time. Consequently, thechanges of the first derivatives of temperature from the first rate ofchange (at portion 604) to the second rate of change (at portions 622and 608) also would not be perceivable. However, the peak 614 of thefirst derivative of temperature for the conductive inclusioncorresponding to the earlier kinks 512 and 514 would be perceivablerelative to values of the first derivative of temperature forsurrounding normal regions.

FIG. 7A illustrates a chart 700 showing a calculated second derivativeof the temperature of the top surface 111 of laminate 110 for the defectfree (i.e., normal) region, indicated by the solid line 702, and to theregion that has the conductive inclusion, discussed above with referenceto FIG. 5A, indicated by the broken line 720. As shown in FIG. 7A, thesecond derivative of temperature for the normal region is zero along afirst portion 704 of the solid line 702 until reaching a first peak 706and then a second opposing peak 708 that corresponds with the kink 506in the temperature plot shown in the chart 500 of FIG. 5A and the rateof change trending from the first rate of change indicated by theportion 604 to the portion 608 (via portion 606) of the solid line 602in FIG. 6A. The second derivative of temperature for the region thatincludes the conductive inclusion results in similar peaks 726 and 728that correspond to the kink 518 in the temperature plot of the chart 500shown in FIG. 5A and the rate of change trending from the first rate ofchange indicated by the portion 604 to the portion 622 (via portion 620)of the broken line 610 in FIG. 6A. The second derivative of temperaturefor the region that includes the conductive inclusion also includes anadditional set of peaks 722 and 724 that correspond with the kinks 512and 514 of the temperature plot shown in FIG. 5A and the rate of changechanging temporarily from the first rate of change indicated by theportion 604 of the solid line 602 to the peak 614 rate of change andthen returning to the first rate of change 604.

As discussed above, in instances in which only a few layers of laminatehave been laid out, the kinks 506 and 518 of the temperature profilesfor the normal regions and conductive inclusions may be perceivable in asuitable period of time for an inspection. In other instances in whichmany layers of laminate have been laid out, the kinks 506 and 518 maynot be perceivable in a suitable period of time. Consequently, the peaks706 and 708 for the normal regions and the peaks 726 and 728 for theconductive inclusion regions, corresponding to the kinks 506 and 518,may not be perceivable in a suitable period of time. However, the peaks722 and 724 of the second derivative of temperature for the conductiveinclusion, corresponding to the earlier kinks 512 and 514, would beperceivable relative to values of the first derivative of temperaturefor surrounding normal regions.

FIG. 5B illustrates the differences in temperature of the top surface111 of the laminate 110 over time for a defect-free region of thelaminate and a region that has a disbond and/or an insulative inclusion.As explained above, an insulative inclusion is an inclusion (e.g.,debris) that conducts heat less readily than the laminate layers. Forexample, a piece of backing paper caught between layers of the laminatecould be an insulative inclusion. After a heat source, such as the heatsource 214 shown in FIG. 2, outputs a burst of energy directed towardthe top surface 111 of the laminate 110, the temperature of the topsurface 111 of the laminate 110 rises. The chart 550 in FIG. 5B includesthe solid line 502 indicating the normal (i.e., defect free) region ofthe laminate and a broken line 560 indicating the region that has adisbond and/or insulative inclusion. The left-hand ends of the solidline 502 and the broken line 560 indicate the temperature of the topsurface 111 of the laminate 110 immediately after the burst of energyfrom the heat source 214 is applied to the top surface 111. Energyabsorbed by the top surface 111 has caused the temperature of the topsurface 111 to increase. After the initial increase in temperature ofthe top surface 111, the temperature of the top surface 111 begins todecrease in a linear manner as the heat energy applied to the topsurface 111 travels deeper into the laminate via conduction (asindicated by first portion 504 of the solid line 502). The initial rateof heat transfer away from the top surface 111 via conduction issubstantially the same for both the normal region and the region thatincludes the inclusion, as indicated by the initial overlap of the solidline 502 and the broken line 560.

Referring to the normal region, indicated by the solid line 502, as theheat energy reaches a bottom side of the laminate 110, the heat energycan travel no further through the laminate via conductance. Thereafter,the heat transfer away from the top surface 111 slows, as indicated bythe kink 506 and the reduced-slope second portion 508 of the solid line502.

Referring to the disbond and/or insulative inclusion region, indicatedby the broken line 560, before the heat energy reaches the bottom sideof the laminate 110, the heat energy encounters the disbond and/orinsulative inclusion (e.g., the inclusion 122 shown in FIG. 1C could bean insulative inclusion). The exemplary disbond and/or insulativeinclusion provides additional mass that can act as a heat sink for thelaminate such that heat from the top surface 111 can be transferred tothe inclusion via conductance. However, because the exemplary disbondand/or insulative inclusion is less conductive than the surroundinglayers of laminate, the top surface 111 of the laminate 110 over thedisbond and/or insulative inclusion cools slower than surroundingregions of the top surface 111. This slower cooling of the top surface111 is indicated by a first kink 562 of the broken line 560 as thebroken line 560 deviates from the solid line 502. Over time, the heattransfer from the top surface 111 increases and the broken line 560 hasa second kink 564. After the second kink 564, the rate of temperaturechange of the top surface 111 over the disbond and/or insulativeinclusion is substantially equal to the rate of temperature change ofthe top surface 111 over normal regions of the laminate 110, asindicated by portion 504 of the solid line 502, as indicated by theportion 566 of the broken line 560. Because the disbond and/orinsulative inclusion transfers heat away from the top surface 111slowly, the heat reaches the back surface of the laminate 110 at thedisbond and/or insulative inclusion slower than at surrounding normalregions. Thereafter, the heat transfer away from the top surface 111over the disbond and/or insulative inclusion slows, as indicated by thekink 568 in the broken line, and eventually joins the second portion ofthe solid line 502.

For a laminate that is only three, four, or five layers thick, the kinks506 and 568 in the temperature profiles for a normal region and a regionthat includes a disbond and/or insulative inclusion may be observable ina reasonable period of time. For example, the kinks 506 and 568 mayoccur within three to ten seconds after heat is applied to the topsurface 111 of the laminate 110. However, in instances in which thelaminate is thicker (e.g., including tens of layers, such as fiftylayers, one hundred layers, or one hundred and fifty layers), the kinks506 and 568 may not be observable in a suitable period of time for suchan inspection. In such instances, the kink 562 and/or the kink 564 inthe temperature profile of the top surface 111 over the disbond and/orinsulative inclusion should be perceivable in a suitable period of time.The kink 506 in the temperature profile of the top surface 111 overnormal regions does not need to be observed. For example, assuming thatmost of the laminate 110 is free from defects, the temperature profileover time would be substantially homogenous. However, if a particularregion includes a disbond and/or insulative inclusion, that region wouldhave a temperature profile that decreases at a slower rate (at the kink562) than the defect free regions. Thus, observing a temperature profiledecreasing at a slower rate than surrounding regions could indicate thepresence of a disbond and/or insulative inclusion in the laminate 110.

FIG. 6B illustrates a chart 650 showing a calculated first derivative ofthe temperature (i.e., a rate of change of temperature) of the topsurface 111 of laminate 110 for the defect free (i.e., normal) region,indicated by the solid line 602, and of the region that has the disbondand/or insulative inclusion, discussed above with reference to FIG. 5B,indicated by the broken line 660. As shown in FIG. 6B, the firstderivative of temperature for the normal region is a first rate ofchange, indicated by portion 604 of the solid line 602, whichcorresponds with the first portion 504 of the solid line 502 in FIG. 5B.Since the temperature of the top surface 111 is decreasing, the valuesof the first derivative are negative. Stated differently, a zero valueon the temperature axis of the chart 650 is above the illustrated solidline 602 and the broken line 610. When the temperature profile of thetop surface 111 over the normal region reaches the kink 506 in FIG. 5B,the first derivative of temperature for the normal region increases(toward zero), as indicated by the portion 606 of the solid line 602.Thereafter, the first derivative of temperature for the normal regionsettles at a second rate of heat transfer, as indicated by the portion608 of the solid line 602. The first derivative of temperature for theregion that includes the disbond and/or insulative inclusion divergesfrom the first derivative of temperature for the normal region twice.First, where the temperature profile of the top surface 111 for thedisbond and/or insulative inclusion decreases slower than surroundnormal regions at the kinks 562 and 564 (in FIG. 5B), the firstderivative of temperature increases (toward zero) from the first rate ofchange (indicated by the portion 604 of the solid line 602) at the pointindicated by reference numeral 662, reaches a peak at the pointindicated by reference numeral 664, and then decreases (away from zero)at the point indicated by reference numeral 666. When the temperatureprofile of the top surface 111 over the disbond and/or insulativeinclusion reaches the kink 568 in FIG. 5B, the first derivative oftemperature increases (toward zero) at the point indicated by referencenumeral 668 and as indicated by the portion 670 of the broken line 660.Thereafter, the first derivative of temperature for the disbond and/orinsulative inclusion settles at the second rate of heat transfer, asindicated by the portion 608 of the solid line 602.

As discussed above, in instances in which only a few layers of laminatehave been laid out, the kinks 506 and 568 of the temperature profilesfor the normal regions and disbond and/or insulative inclusions may beperceivable in a suitable period of time for an inspection. In otherinstances in which many layers of laminate have been laid out, the kinks506 and 568 may not be perceivable in a suitable period of time.Consequently, the changes of the first derivatives of temperature fromthe first rate of change (at portion 604) to the second rate of change(at portion 608) also would not be perceivable. However, the peak 664 ofthe first derivative of temperature for the disbond and/or insulativeinclusion corresponding to the earlier kinks 562 and 564 would beperceivable relative to values of the first derivative of temperaturefor surrounding normal regions.

FIG. 7B illustrates a chart 750 showing a calculated second derivativeof the temperature of the top surface 111 of laminate 110 for the defectfree (i.e., normal) region, indicated by the solid line 702, and to theregion that has the disbond and/or insulative inclusion, discussed abovewith reference to FIG. 5B, indicated by the broken line 760. As shown inFIG. 7B, the second derivative of temperature for the normal region iszero along a first portion 704 of the solid line 702 until reaching afirst peak 706 and then a second opposing peak 708 that corresponds withthe kink 506 in the temperature plot shown in the chart 550 of FIG. 5Band the rate of change trending from the first rate of change indicatedby the portion 604 to the portion 608 (via portion 606) of the solidline 602 in FIG. 6B. The second derivative of temperature for the regionthat includes the disbond and/or insulative inclusion results in similarpeaks 766 and 768 that correspond to the kink 568 in the temperatureplot of the chart 550 shown in FIG. 5B and the rate of change trendingfrom the first rate of change indicated by the portion 604 to theportion 622 (via portion 620) of the broken line 660 in FIG. 6B. Thesecond derivative of temperature for the region that includes thedisbond and/or insulative inclusion also includes an additional set ofpeaks 762 and 764 that correspond with the kinks 562 and 564 of thetemperature plot shown in FIG. 5B and the rate of change changingtemporarily from the first rate of change indicated by the portion 604of the solid line 602 to the peak 664 rate of change and then returningto the first rate of change of the solid line 604.

As discussed above, in instances in which only a few layers of laminatehave been laid out, the kinks 506 and 568 of the temperature profilesfor the normal regions and disbond and/or insulative inclusions may beperceivable in a suitable period of time for an inspection. In otherinstances in which many layers of laminate have been laid out, the kinks506 and 568 may not be perceivable in a suitable period of time.Consequently, the peaks 706 and 708 for the normal regions and the peaks766 and 768 for the disbond and/or insulative inclusion regions,corresponding to the kinks 506 and 568, may not be perceivable in asuitable period of time. However, the peaks 762 and 764 of the secondderivative of temperature for the disbond and/or insulative inclusion,corresponding to the earlier kinks 562 and 564, would be perceivablerelative to values of the first derivative of temperature forsurrounding normal regions.

In instances in which the laminate 110 includes a neutral inclusion(e.g., an inclusion with the same heat transfer characteristics as theplies of the laminate, such as a scrap of another ply), such a neutralinclusion may be detectable if it occurs in the first several layers ofa laminate. Such a neutral inclusion may include disbonds surroundingit. For example, the inclusion 122 shown in FIG. 1C includes disbonds124 (i.e., voids or air gaps) in regions immediately surrounding theinclusion. Such disbonds 124 may be detectable as discussed above withreference to FIGS. 5B, 6B, and 7B.

Referring again to FIG. 2, in use, the heat transfer detection program226 executing on the computer processor 222 could evaluate thetemperature, first derivative of temperature, and/or second derivativeof temperature for every pixel of every image stored in memory 224 fromthe digital thermographic camera 212. Pixels or regions of pixels thathave different heat characteristics then surrounding pixels or regionscould be identified as regions containing defects, and the defects couldbe addressed, as discussed above with reference to FIGS. 3 and 4. Inaspects of the system 200 in which the digital thermographic camera 212has a view of the entire laminate 110, each pixel of a digitalthermographic image captured by the digital thermographic camera 212corresponds to a particular region of the laminate 110. Thus, defects inthe laminate 110, detected in pixels or regions of pixels in the digitalthermographic images, can be located by finding the location(s) on thelaminate 110 corresponding to the pixels that indicate the defect(s).

In various aspects of the system, the digital thermographic camera 212may not capture an image of the entire laminate 110. In such aspects,the digital thermographic camera 212 and the heat source 214 may move inthe directions of arrows 216 and/or 218 to capture images of differentportions of the laminate 110. At least one aspect, the digitalthermographic camera 212 and heat source 214 could continuously movewhile the heat source 214 applies heat to the top surface 111 oflaminate 110 and the digital thermographic camera 212 captures digitalthermographic images of the temperature of the top surface 111 of thelaminate 110. In such aspects, the system 200 could map the pixels ofthe image to locations on the laminate 110 as described in U.S.application Ser. No. 14/614,198, filed on Feb. 16, 2015, and entitled“system and method for high-speed FOD detection,” the entire contents ofwhich are incorporated by reference herein.

The system 200 could include one of several different combinations ofdigital thermographic camera 212 and heat source 214. For example, thedigital thermographic camera 212 and heat source 214 could be includedin a single unit such as the Thermoscope® II manufactured by ThermalWave Imaging. In at least one test, a similar thermal wave imagingsystem was able to detect an inclusion under two or three layers ofuncured compacted composite sheets. As another example, the VoyageIR® 2thermal processing system by Thermal Wave Imaging combines the digitalthermographic camera 212 and heat source 214 into a single unit and, inat least one test, was able to detect an inclusion under two or threelayers of uncured compacted composite sheets. As another example, aThermaCam™ SC640 infrared camera by FLIR Systems® could be used as thedigital thermographic camera 212, and could be used in combination witha heat source 212, such as a heat gun or lamp. In at least one test,such an infrared camera was able to detect an inclusion under one layerof uncured compacted composite sheet. As yet another example, an E40infrared camera by FLIR Systems® could be used as the digitalthermographic camera 212, and could be used in combination with a heatsource 212, such as a heat gun or lamp. In at least one test, such aninfrared camera was able to detect an inclusion under one layer ofuncured compacted composite sheet.

FIG. 8 is a flow chart of a process 800 for detecting a defect accordingto another aspect of the disclosure. Process 800 is similar to process300. However, process 800 performs flaw detection analysis after eachply of material is laid down. Therefore, process 800 allows defects tobe identified before additional plies are positioned thereon, thusresulting in more simplified repair processes. Additionally, ininstances where a defect is determined to be beyond repair, the ply (orentire workpiece) can be scrapped, rather than completing layup ofadditional plies. In such an example, materials are not wasted onunusable plies or workpieces, thereby resulting in cost savings.

Process 800 begins at block 801. At block 801, an uncured ply ofmaterial, such as a composite material described herein, is laid down.The uncured ply of material may be one of multiple plies of a workpiece,such as an aircraft part or component. At block 802, the ply of materialis inspected, for example, by infrared thermography. Infraredthermography inspection includes subjecting the uncured ply to a burstof thermal energy, and capturing at least one digital thermographicimage of the surface of the uncured ply, as described above. In such anexample, inspection may be a full line scan or a flash scan. Tofacilitate data collection, it is contemplated that a digitalthermographic camera 212 (shown in FIG. 2) for imaging thethermally-subjected ply may be positioned on a fabrication headconfigured to lay the uncured ply of material.

Optionally, other optical inspections may be performed during block 802.The optical inspections include one or more of laser line scans,high-resolution video, or other non-contact sensing of the ply. Theoptical data and the infrared thermography data are subsequently storedin a memory. In one example, the optical data is correlated to theinfrared thermography data based on, for example, part geometry. Tofacilitate correlation, a CAD model or other digital representation maybe utilized.

In block 803, inspection data captured during block 802 is analyzed todetermine the presence of defects in or immediately beneath the uncuredply laid down in block 801. The analysis in block 803 includes comparingcaptured inspection data to rejection criteria, such as baseline data,to facilitate identification of inspection data from block 802 that isout of a desired range. The baseline data may include inspection data ofprevious plies of known acceptable quality, or may includeoperator-input data or ranges. In one example, the baseline data mayinclude thermal data to which captured data (e.g., data from block 802)is compared. By comparing the data of block 802 to the rejectioncriteria, defects, foreign objects and debris (FOD), missing plies,geometry-tolerance errors, and the like can be identified. It iscontemplated that the analysis of block 803 may occur automatically,that is, without specific operator input.

In block 804, a determination is made by a controller as to whether arejectable flaw (e.g., a flaw outside of a predetermined acceptablequality range) is identified in block 803. In one example, a rejectableflaw is determined to exist if a threshold variance is exceeded whencomparing baseline data to captured data. If the determination in block804 is affirmative, process 800 proceeds to block 805, in whichadditional assessment is performed. In block 805, a model-basedassessment is performed to determine the effect of the rejectable flaw.The model-based assessment determines the effect of the rejectable flawwith respect to structure, thermal, adhesive, or other qualities. In oneexample, it is contemplated that model-based assessments may becatalogued, and used for subsequent assessments, when similar, therebyreducing processing time by mitigating computations from the analysis.

After block 805, a determination is made in block 806 as to whether theply (or workpiece) having the rejectable flaw is usable as-is. If theply or workpiece having the rejectable flaw is unusable, production isstopped in block 807. In block 808, an operator is signaled thatproduction has stopped and/or that an unusable ply has been identified.In block 809, the rejectable flaw is repaired. Example repair processesare discussed above, but are not to be considered limiting. In oneexample, flaw repair may include FOD removal, ply removal, defectrepair, and the like. Because the rejectable flaw is repaired beforelaying additional plies on the workpiece, the rejectable flaw isrelatively easy to access, thereby simplifying the repair processes andresulting in a less time-consuming or less-costly repair. Additionally,in the repair operation of block 809, an operator can rely oninformation obtained in block 802 and 803, thereby further simplifyingthe repair process by providing the operator with more accurate and morecomplete information for completing the repair. For example, precisegeometric coordinates of the flaw may be provided, thereby aiding inidentification and/or repair of the flaw by the repairing operator.

After the repair processes have been completed, the repaired ply isre-inspected in block 810. The re-inspection processes may be asthorough as the inspection of block 802, or the re-inspection may belimited reinspection that focuses only on the repaired area, or thatotherwise performs limited analysis, such as less than all inspectionsperformed in block 802. Upon completion of operation 810, the inspectiondata for the workpiece/ply obtained in block 802 is updated to includethe reinspection data of block 810 in order to provide comprehensivemonitoring of the ply.

Returning to block 804, if no rejectable flaws are found, then process800 proceeds to block 811. In block 811, any identified sub-rejectableflaws (from block 803) are recorded in a memory by a controller or otherprocessing unit. Sub-rejectable flaws include flaws outside of apredetermined quality range, but not rising to a level of a rejectableflaw. Recording of one or more of the location, type, and extent of thenon-rejectable flaw facilitates tracking and monitoring of thenon-rejectable flaw during additional processing, such as the placementof additional plies on the workpiece. Thus, should the non-rejectableflaw become (or generate) a rejectable flaw during future processing,the rejectable flaw can more easily be identified. In one example, it iscontemplated that one or more process conditions of future processes(such as laying of future plies) are adjusted, manually orautomatically, to compensate and/or mitigate flaw exacerbation ofsub-rejectable flaws. Thus, it is possible to reduce the likelihood thatsub-rejectable flaws become rejectable flaws. In addition, if acontroller detects of pattern of reoccurring rejectable orsub-rejectable flaws on workpieces, the controller may facilitate anadjustment to an upstream production process to mitigate or eliminatereoccurring flaw on future plies or workpieces.

In block 812, a determination is made as to whether a final ply has beenlaid. If the final ply has not been laid on the workpiece, process 800returns to block 801. If the final ply has been laid, process 800proceeds to block 813, and a curing operation is performed on the one ormore plies of the workpiece. The curing operation of block 812 issimilar to the curing operations of block 312 (shown in FIG. 3) and/orblock 416 (shown in FIG. 4) discussed above. After curing, an optionalpost-cure inspection may be performed in block 814. The post-cureinspection may be a complete inspection, or a partial inspection, suchas only on a selected area. In one example, the selected area is an areain which a rejectable flaw or a sub-rejectable flaw has been previouslyidentified. Whether or not a post-cure inspection is performed may bedictated by the number of rejectable flaws and/or non-rejectable flawsidentified during processing, among other factors.

FIG. 8 illustrates one example of a process 800. However, other examplesand modifications are contemplated. In one example, it is contemplatedthat inspection data acquired in block 802 for a ply in which norejectable flaws or sub-rejectable flaws are found may be used to updatethe baseline data used in block 803, for example, by combining the dataacquired with block 802 and determining an average, or alternatively,but adjusting a range of the baseline data which indicates acceptableprocessing. Thus, the baseline data becomes refined and more accurate(via a larger sample size) as processing proceeds. In such an example,it is contemplated that the baseline data may be correlated to a CADmodel. In another example, all data collected for plies which remain inthe workpiece (including plies having sub-rejectable flaws) is stored tofacilitate trend analysis, tool/part redesign, process modifications,and the like.

The descriptions of the various aspects have been presented for purposesof illustration, but are not intended to be exhaustive or limited to theaspects disclosed. Many modifications and variations will be apparent tothose of ordinary skill in the art without departing from the scope andspirit of the described aspects. The terminology used herein was chosento best explain the principles of the aspects, the practical applicationor technical improvement over technologies found in the marketplace, orto enable others of ordinary skill in the art to understand the aspectsdisclosed herein.

Aspects described herein may take the form of an entirely hardwareaspect, an entirely software aspect (including firmware, residentsoftware, micro-code, etc.) or an aspect combining software and hardwareaspects that may all generally be referred to herein as a “circuit,”“module” or “system.”

Aspects described herein may be a system, a method, and/or a computerprogram product. The computer program product may include a computerreadable storage medium (or media) having computer readable programinstructions thereon for causing a processor to carry out aspectsdescribed herein.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operationsdescribed herein may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some aspects, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects described herein.

Aspects are described herein with reference to flowchart illustrationsand/or block diagrams of methods, apparatus (systems), and computerprogram products according to aspects. It will be understood that eachblock of the flowchart illustrations and/or block diagrams, andcombinations of blocks in the flowchart illustrations and/or blockdiagrams, can be implemented by computer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousaspects described herein. In this regard, each block in the flowchart orblock diagrams may represent a module, segment, or portion ofinstructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

Aspects described herein may be provided to end users through a cloudcomputing infrastructure. Cloud computing generally refers to theprovision of scalable computing resources as a service over a network.More formally, cloud computing may be defined as a computing capabilitythat provides an abstraction between the computing resource and itsunderlying technical architecture (e.g., servers, storage, networks),enabling convenient, on-demand network access to a shared pool ofconfigurable computing resources that can be rapidly provisioned andreleased with minimal management effort or service provider interaction.Thus, cloud computing allows a user to access virtual computingresources (e.g., storage, data, applications, and even completevirtualized computing systems) in “the cloud,” without regard for theunderlying physical systems (or locations of those systems) used toprovide the computing resources.

Typically, cloud computing resources are provided to a user on apay-per-use basis, where users are charged only for the computingresources actually used (e.g. an amount of storage space consumed by auser or a number of virtualized systems instantiated by the user). Auser can access any of the resources that reside in the cloud at anytime, and from anywhere across the Internet. In context of at least oneaspect, a user may access applications (e.g., the heat transferdetection program 226) or related data available in the cloud. Forexample, the heat transfer detection program 226 could execute on acomputing system in the cloud and detect defects, such as disbondsand/or inclusions in uncured compacted layers of composite sheets. Insuch a case, the heat transfer detection program 226 could analyzeimages captured by the digital thermographic camera 212 and store theanalysis of the images at a storage location in the cloud. Doing soallows a user to access this information from any computing systemattached to a network connected to the cloud (e.g., the Internet).

While the foregoing is directed to certain aspects, other and furtheraspects may be devised without departing from the basic scope thereof,and the scope thereof is determined by the claims that follow.

What is claimed is:
 1. A method, comprising: laying a first ply ofmaterial; applying thermal energy to a surface of the first ply ofmaterial; capturing at least one digital thermographic image of thesurface of the first ply of material after applying the thermal energy;using a computer processor, analyzing at least one heat characteristicof regions of the first ply of material in the at least one digitalthermographic image to identify defect regions in which the at least oneheat characteristic is different than baseline data; based on theanalyzing, making a determination as to whether the defect regionincludes a rejectable flaw or a sub-rejectable flaw, wherein: uponidentifying a defect region including a rejectable flaw: outputting analert; halting processing to allow the defect region to be corrected;resuming processing; and laying a second ply of material on the firstply of material after resuming processing; and upon identifying a defectregion including a sub-rejectable flaw: laying a second ply of materialon the first ply of material while the sub-rejectable flaw remains inthe first ply of material.
 2. The method of claim 1, further comprisingcuring the first ply of material and the second ply of material afterlaying the second ply of material.
 3. The method of claim 1, whereinanalyzing at least one heat characteristic in the at least one digitalthermographic image comprises analyzing at least one heat characteristicof every pixel in the at least one digital thermographic image.
 4. Themethod of claim 1, wherein the at least one heat characteristiccomprises at least one of respective temperatures of the regions,respective first derivative rates of change of temperature of theregions over a plurality of digital thermographic images, and respectivesecond derivative rates of change of temperature of the regions over aplurality of digital thermographic images, and wherein the at least oneheat characteristic of a subject region is different than surroundingregions if a peak of a second derivative rate of change of temperaturefor the subject region differs in time from a peak of a secondderivative rate of change of temperature of at least one surroundingregions by more than a threshold amount.
 5. The method of claim 1,further comprising: determining that the second ply of material does notinclude a defect; and updating the baseline data based on a digitalthermographic image of a surface of the second ply of material.
 6. Themethod of claim 1, further comprising reinspecting the first ply ofmaterial after resuming processing.
 7. The method of claim 1, whereinthe alert includes an indication of a location of the defect region onthe first ply of material.
 8. The method of claim 1, wherein making thedetermination as to whether the defect region includes a rejectable flawor a sub-rejectable flaw comprises performing a model-based assessmentthat determines the effect of the defect region with respect to one ormore of structural, thermal, or adhesive qualities.
 9. A system,comprising: a work surface for arranging and compacting uncuredcomposite layers; a heat source arranged relative to the surface andoperable to provide thermal energy to a surface of a first ply ofmaterial on the work surface; a thermographic digital camera arrangedrelative to the surface and operable to capture at least one digitalthermographic image of the surface of the first ply of material; acomputer processor in communication with the thermographic digitalcamera and the heat source; and a computer memory containing a programthat, when executed on the computer processor, performs an operation forprocessing data, comprising: applying thermal energy to a surface of thefirst ply of material; capturing at least one digital thermographicimage of the surface of the first ply of material after applying thethermal energy; analyzing at least one heat characteristic of regions ofthe first ply of material in the at least one digital thermographicimage to identify defect regions in which the at least one heatcharacteristic is different than baseline data; based on the analyzing,making a determination as to whether the defect region includes arejectable flaw or a sub-rejectable flaw, wherein: upon identifying adefect region including a rejectable flaw: outputting an alert; haltingprocessing to allow the defect region to be corrected; resumingprocessing; and laying a second ply of material on the first ply ofmaterial after resuming processing; and upon identifying a defect regionincluding a sub-resectable flaw: laying a second ply of material on thefirst ply of material while the sub-rejectable flaw remains in the firstply of material.
 10. The system of claim 9, wherein the program, whenexecuted on the computer processor, performs an additional operation forprocessing data, comprising, upon receiving an indication of acorrection being made to the defect region: outputting a second signalto the heat source to apply a second thermal energy to the surface ofthe first ply; capturing a second at least one digital thermographicimage of the surface of the first ply after applying the second thermalenergy; analyzing at least one heat characteristic of regions of thefirst ply in the second at least one digital thermographic image toidentify defect regions in which the at least one heat characteristic isdifferent than surrounding regions.
 11. The system of claim 9, whereinanalyzing at least one heat characteristic of the first ply in the atleast one digital thermographic image to identify regions in which theat least one heat characteristic is different than surrounding regionscomprises analyzing at least one heat characteristic of every pixel inthe at least one digital thermographic image.
 12. The system of claim 9,wherein the at least one heat characteristic of the first ply comprisesat least one of respective temperatures of the regions, respective firstderivative rates of change of temperature of the regions over aplurality of digital thermographic images, and respective secondderivative rates of change of temperature of the regions over aplurality of digital thermographic images.
 13. The system of claim 12,wherein the at least one heat characteristic of a subject region isdifferent than surrounding regions if a peak of a second derivative rateof change of temperature for the subject region differs in time from apeak of a second derivative rate of change of temperature of at leastone surrounding regions by more than a threshold amount.
 14. The systemof claim 8, wherein the alert includes an indication of a location ofthe defect region.
 15. A method, comprising: laying a first ply ofmaterial; applying thermal energy to a surface of the first ply ofmaterial; capturing at least one digital thermographic image of thesurface of the first ply of material after applying the thermal energy;using a computer processor, analyzing at least one heat characteristicof regions of the first ply of material in the at least one digitalthermographic image to identify defect regions in which the at least oneheat characteristic is different than baseline data; based on theanalyzing, making a determination as to whether the defect regionincludes a rejectable flaw or a sub-rejectable flaw, wherein: uponidentifying a defect region including a rejectable flaw: outputting analert; correcting the defect region; and laying a second ply of materialon the first ply of material after correcting the defect region; andupon identifying a defect region including a sub-rejectable flaw: layinga second ply of material on the first ply of material while thesub-rejectable flaw remains in the first ply of material.
 16. The methodof claim 15, further comprising: capturing a digital thermographic imageof a surface of the second ply of material; and comparing the digitalthermographic image of a surface of the second ply of material to thebaseline data.
 17. The method of claim 16, wherein comparing the digitalthermographic image of a surface of the second ply of material to thebaseline data comprises determining whether a rejectable flaw exists anddetermining whether a sub-rejectable flaw exists.
 18. The method ofclaim 17, wherein if a sub-rejectable flaw exists, further comprisinglaying a third ply of material on the second ply of material withoutissuing an alert or without halting processing.
 19. The method of claim15, further comprising: determining that the second ply of material doesnot include a defect; and updating the baseline model based on thedigital thermographic image of a surface of the second ply of material.20. The method of claim 15, further comprising reinspecting the firstply of material after correcting the defect and before laying the secondply of material.